The present invention relates to the packaging of liquid materials in flexible bags made of synthetic plastic sheet material formed into flat bags comprising relatively closely spaced confronting walls joined and sealed together at the margins thereof to form a sealed enclosed space.
Flat flexible bags are used for packaging liquid or solid materials. When holding liquid materials such a bag may be so completely filled with a liquid that the walls thereof are bulged by the liquid for all orientations of the bag. In other cases, when the bag is partially filled with liquid when held upright, it may act as a filled bag when lying horizontally, since the volume of the space in such a bag is much less when the bag lies flat on a horizontal support surface where gravity causes the walls thereof to be more closely spaced than when the bag is held upright. The bag walls are then bulged outwardly by the volume of the liquid therein. In both cases, the bags must be made of sufficient strength that when packed one above the other in boxes for storage or shipment, they can support the weight of the maximum possible number of bags which may be stacked above the same without rupturing under the weight involved. The force applied to the walls of a bag in such a box is, in part, dependent on the weight of the liquid in each bag and the number of bags which are stacked above it. Normally, these bags readily can withstand these forces. However, these forces are increased manyfold when the box is dropped inadvertently upon a floor, for example, at a height of several feet and not infrequently the lowermost bags in the box rupture under the forces involved. To avoid this problem, the bags must be made of such thick sheet stock that the cost of the bags becomes excessive.
It is, accordingly, an object of the invention materially to increase the rupture strength of flat bags as described without the need of increasing the thickness of the bag walls, so that the bags can withstand the substantial impact forces applied thereto when they constitute the bottommost bags in boxes which may be dropped inadvertently upon the floor.
Another object of the invention is to provide a flexible bag as described wherein the liquid contents of the bag can be quickly and easily poured from the bag without requiring any squeezing of the bag in the process of pouring the liquid from the bag.
A further object of the invention is to provide a partially filled bag as described wherein the bag per se is a conventionally constructed inexpensive bag with a wall thickness which normally would pose a risk of rupturing under the circumstances described.
To my knowledge, the prior art has not developed flat flexible bags satisfying these objectives. U.S. Pat. No. 3,433,353 discloses a container made from relatively thick thermoplastic-sheet stock which is shaped in such a way as to maximize the impact strength of the container when dropped from considerable heights. U.S. Pat. No. 3,340,669 discloses a flat flexible bag of a special configuration for protecting frangible articles. The bags or containers disclosed in these patents are of complex and expensive construction and do not satisfy the objectives of the present invention.